1. Field of the Invention
This invention pertains generally to the field of Asynchronous Transfer Mode (ATM) switching, and in particular to a shared memory to provide temporary storage of inputs which contend for the same output. Specifically, this invention describes a shared memory ATM switch where the memory is controlled with a content addressable memory (CAM).
2. Description of the Prior Art
Asynchronous Transfer Mode (ATM) switching requires a memory to provide temporary storage of inputs which contend for the same output. Proposed architectures consist of input storage, output storage or shared memory. It has been shown that shared memory architectures provide minimum cell loss probability for a given memory size. However, a shared memory creates a complex memory management problem with time consuming operations since the switch must know the cell location of different inputs, outputs and priorities.
The major requirement in ATM switch fabrics is to deliver the cells to the desired output port with minimum cell loss and minimum delay. Since cells from multiple inputs may be destined for the same output, the cells must be stored in a memory (buffer) until they can be sent to the output. If multiple inputs contend for the same output for a long time, a finite size buffer can overflow and cells are lost. Therefore, efficient buffer management is very important in minimizing cell loss in ATM switch fabrics.
Many papers have been published in the literature on memory management control in ATM switching. One control method uses look-up tables which serve as a directory for cell location in the buffer memory Takahiko Kozaki, et al, "32.times.32 Shared Buffer Type ATM Switch VLSI's for B-ISDN's, "IEEE Journal on Selected Areas in Communications, Vol. 9, No. 8, October 1991.!. The disadvantage of this method is that a switch with N inputs and L priorities requires NxL look-up tables. This plus associated control consumes a significant portion of the chip area. Another memory management control technique uses a linked list where each cell contains the location of the next cell Clark B. Woodworth, "A Flexible Broadband Packet Switch for a Multimedia Integrated Network," ICC 91; Manolis Katevenis, et al, "Weighted Round-Robin Cell Multiplexing in a General-Purpose ATM Switch Chip," IEEE Journal on selected areas in Communications, Vol. 9, No. 8. October 1991!. This scheme has a potential reliability problem since the corruption of one cell can result in a complete breakdown in cell sequence.
It is the principal object of this invention to provide an ATM switch architecture which uses a Content Addressable Memory (CAM) to control the buffer that stores the ATM cells. In this scheme the ID of each cell is stored in the CAM which is interrogated during cell retrieval. CAM-control is reliable, fast, area efficient, and provides extreme flexibility in manipulating cells.
Another object of the invention is to provide an ATM switch with a fully shared memory, and which uses a Content Addressable Memory (CAM) to control the buffer that stores the ATM cells.
It is still a further object of this invention to provide an ATM switch with an output buffered memory, and which uses a Content Addressable Memory (CAM) to control the buffer that stores the ATM cells.